1977 Volume 46 Issue 3 Pages 352-360
Difference of the thermo-response of heading date, number of main culm leaves and leaf emergence intervals between the culture using mature seedling (5th leaf stage) and the culture using young seedling (2nd leaf stage) have been investigated with 36 paddy rice cultivers of various maturities under five different levels of temperature in semi-open air controlling cabinets. Air temperature in the rice community in the cabinets were kept at 3°C, 1.5°C and 0°C warmer, and 1.5°C and 3°C cooler than that of the open air as an average during rice cultivated period in Morioka (Iwate) in 1974 (Fig. 5). The heading response in varieties to the temperature in culture using mature seedling and that using young seedling were explained in terms of number of main culm leaves and leaf emergence intervals in the following way. 1. The difference of leaf age in varieties among each thermo-condition was larger in culture using young seedling than in culture using mature seedling (Fig. 4), and the response of total leaf number on main culm of varieties to temperatures was a little higher in culture using young seedling than in culture using mature seedling (Table 3). In consequence, the fluctuation in heading of varieties by temperature was larger in culture using young seedling than in culture using mature seedling (Fig. 1). 2. The difference of total leaf number between two cultural methods was larger in late varieties than in early varieties, and was larger under high temperature than low temperature (Table 3). The difference of leaf age of varieties between two culture methods was a little larger under low temperature than under high temperature (Fig. 4). From these results, the difference of heading date between two culture methods was larger in early varieties than in late varieties, and was larger low temperature than under high temperature (Table 1, Fig. 5). From these facts, it can be said that the risk of cool weather damage increase futher in rice culture using young seedling.
